1. Field of the Invention
The present invention, in general, relates to a composition comprising powdered carbonaceous adsorbent suspended in a branched hydrocarbon solvent. Additionally, this invention relates to a process for removing organic pollutants comprising predominantly nonbiodegradable organic compounds from waste waters by contacting said waste waters, under adsorption conditions, with a slurry of powdered carbonaceous adsorbent suspended in a hydrocarbon solvent.
2. Description of the Prior Art
The most common method presently employed for removing impurities from waste water includes a primary settling step wherein a major portion of the solids suspended in the waste water is removed with or without the aid of chemical floculating agents followed by a secondary treating step wherein the remaining suspended solids as well as soluble organic material are decomposed by bacteriological action. The effluent from the secondary treating step is then settled to remove the bacteria and the sludge. Thereafter, the clarified effluent is passed into rivers or streams, generally with no further purification, while at least a portion of the sludge is recycled to the secondary treating zone.
This method of biologically treating waste water was developed primarily for the treatment of sanitary or household sewage, which is typically found in a municipal sewer, and has, in general, proven satisfactory provided a high degree of purification is not desired. However, when industrial plants discharge waste waters into municipal sewer systems, serious difficulties may arise since such waste waters often contain a significant amount of nonbiodegradable pollutants and toxic materials. These nonbiodegradable pollutants are not removed from the industrial waste waters and the toxic materials contained therein destroy bacteria in the secondary biological treatment step, thereby rendering the treatment plant inoperable for a period of time while the toxic materials are purged from the system and new bacterial growth re-established. Thus, it is not surprising that relatively large amounts of nonbiodegradable organic compounds may be present in industrial waste waters after the biological secondary treatment. Accordingly, it can be seen that the removal of nonbiodegradable impurities from industrial waste waters may require further treating (for example, with activated carbon) of the effluents from biological secondary treatment plants in order to remove both biodegradable and nonbiodegradable organic contaminants therefrom. Alternatively, it may be desirable to use activated carbon for secondary treatment of the waste waters instead of biological treatment (see, for example, U.S. Pat. Nos. 3,244,621 and 3,455,820, the disclosures of which are incorporated herein by reference).
However, in general, methods of employing conventional activated carbons to remove contaminants from waste water have met with only limited commercial success due to either limited adsorption capability or the high cost of adsorption and regeneration. Also, the high attrition and regeneration losses which occur when activated carbon is employed results in high carbon makeup costs. Conventional activated carbons have the further disadvantage that the adsorbed pollutants are destroyed during regeneration such that they cannot be recovered as a by-product from the process should such be desired.
Usually activated carbon is employed in either granular or powdered form. Activated carbons in powdered form are available at relatively low initial cost since they are produced largely by the partial incineration of waste liquors from paper manufacture. Also, they show faster rates of contaminant removal than the granular form. However, powdered carbon is difficult to use in a continuous process because the powdered carbon is not easily removed from the treated water (due to its highly subdivided state) which results in very low settling rates. In addition, carbon utilization is low relative to granular activated carbon due to the batch contacting.
Granular activated carbons, such as those produced from coal, are expensive adsorbents because they require a multistep process for their manufacture in order to produce them with uniform particle size and acceptable strength and hardness. In addition, the attrition resistance of granular activated carbon is relatively poor and a significant portion of the carbon is lost due to attrition in the handling and use of the material. This may occur, for example, when the spent granular activated carbon is removed from the waste water contacting beds and regenerated, the regenerated carbon then being recycled to the contacting beds. Not only does this represent a high operating cost due to the makeup of the fresh granulated activated carbon, but the fines produced by said attrition are difficult to remove from the treated waste water, and, therefore, represent a source of contamination. Also, waste water treating processes employing granular activated carbon are limited in that it is necessary to inhibit the motion of the carbon granules in order to minimize the attrition of same due to the fragility of the carbon. Furthermore, low rates of contaminant adsorption have been experienced with granular activated carbon relative to powdered activated carbon.
Yet another method for removing contaminants from waste water is by extraction with a hydrocarbon or other solvent (see, for example, Orville C. Sandall et al, AIChE Symposium Series, Vol. 70, pp. 144,1974; V. Lowenstein-Lom et al, Petroleum, pp. 82-84, April 1974; and J. P. Earhart et al, Chemical Engineering Progress, Vol. 73, No. 5, pp. 67-73, 1977, the disclosures of which are incorporated herein by reference). However, solvents have the disadvantage of low capacity for removing dissolved organics from waste waters.
It has also been suggested to transport activated carbon (see japanese application 74/23703, the disclosures of which is incorporated herein by reference) or activated petroleum fluid coke (see U.S. Pat. No. 4,053,396, the disclosure of which is incorporated herein by reference) as a concentrated slurry suspended in water. In addition, suspensions of carbon in paraffinic hydrocarbons (see, for example, Journal of Physical Chemistry, Vol. 44, pp. 652-670 [1940]; Journal of Colloid and Interface Science, Vol. 33, No. 3, pp. 406-420 [1970], the disclosures of which are incorporated herein by reference) as well as suspensions of carbon in nonparaffinic hydrocarbons (see, for example, Analytical Chemistry, Vol. 25, pp. 1390-1393 [1953]; Journal of Colloid Science, Vol. 7, pp. 600-615 [1952]Journal of Colloid Science, Vol. 8, pp. 38-52 [1953]; U.S. Pat. Nos. 2,668,757 and 2,754,267, British Pat. No. 1,304,017, the disclosures all of which are incorporated herein by reference) have been suggested, but not for treating waste waters.
However, it is believed that none of the foregoing prior art discloses the particular suspension described hereinafter nor its use in waste water treating processes.